Magnesium-based alloys containing more than 85% by weight of magnesium may be formed into useful shaped articles for automotive applications. The low density of such formed magnesium articles offers opportunity for vehicle mass reduction and significant improvement in vehicle fuel economy. However, Mg alloys exhibit poor corrosion resistance, both to general corrosion and to galvanic corrosion when in contact with a dissimilar metal. Such poor resistance to corrosion, particularly to galvanic corrosion, significantly limits their wider application, for example as stamped components in automobile bodies which commonly incorporate steel and aluminum.
In many instances, the corrosion resistance of an article may be enhanced by application of one or more barrier coatings, intended to exclude the corrosive environment from contact with the article and so better ensure product longevity in corrosive environments. In auto body manufacture such coatings, which may include paints and other organic coatings, are often applied to an assembled automobile body. In principle such an approach is applicable to magnesium alloys also, but magnesium alloys are not particularly compatible with many commonly-used automobile body coating processes.
What is therefore needed is an efficient and easily-operated technique to modify the surface composition of magnesium alloy components in particular to render such components more corrosion-resistant.